Collapse same-color mixed filament regions across painted areas

Resolve ordinary mixed-filament painted regions to their effective physical
filament on each layer so adjacent same-color zones can merge into one
continuous area instead of being sliced as separate islands.

Add a global "Collapse same-color mixed regions" option, enabled by default,
and automatically turn it off when Local Z dithering is enabled while still
allowing manual re-enable for experimental use.

src/libslic3r/MixedFilament.cpp

@@ -1321,6 +1321,43 @@ unsigned int MixedFilamentManager::resolve_perimeter(unsigned int filament_id,
     return resolve(filament_id, num_physical, layer_index, layer_print_z, layer_height, force_height_weighted);
 }
 
+unsigned int MixedFilamentManager::effective_painted_region_filament_id(unsigned int filament_id,
+                                                                        size_t       num_physical,
+                                                                        int          layer_index,
+                                                                        float        layer_print_z,
+                                                                        float        layer_height,
+                                                                        float        layer_height_a,
+                                                                        float        layer_height_b,
+                                                                        float        base_layer_height) const
+{
+    const int mixed_idx = mixed_index_from_filament_id(filament_id, num_physical);
+    if (mixed_idx < 0)
+        return filament_id;
+
+    const MixedFilament &mf = m_mixed[size_t(mixed_idx)];
+    if (mf.distribution_mode == int(MixedFilament::SameLayerPointillisme))
+        return filament_id;
+
+    const std::string normalized_pattern = normalize_manual_pattern(mf.manual_pattern);
+    if (normalized_pattern.find(',') != std::string::npos)
+        return filament_id;
+
+    const bool is_custom_mixed = mf.custom;
+    if (!is_custom_mixed && (layer_height_a > 0.f || layer_height_b > 0.f)) {
+        const float safe_base = std::max<float>(0.01f, base_layer_height);
+        const int ratio_a = std::max(1, int(std::lround((layer_height_a > 0.f ? layer_height_a : safe_base) / safe_base)));
+        const int ratio_b = std::max(1, int(std::lround((layer_height_b > 0.f ? layer_height_b : safe_base) / safe_base)));
+        const int cycle   = ratio_a + ratio_b;
+
+        if (cycle > 0) {
+            const int pos = ((layer_index % cycle) + cycle) % cycle;
+            return pos < ratio_a ? mf.component_a : mf.component_b;
+        }
+    }
+
+    return resolve(filament_id, num_physical, layer_index, layer_print_z, layer_height);
+}
+
 std::vector<unsigned int> MixedFilamentManager::ordered_perimeter_extruders(unsigned int filament_id,
                                                                             size_t       num_physical,
                                                                             int          layer_index,

src/libslic3r/MixedFilament.hpp

@@ -179,6 +179,18 @@ public:
                                    float        layer_print_z = 0.f,
                                    float        layer_height  = 0.f,
                                    bool         force_height_weighted = false) const;
+    // Resolve the filament ID that should own painted regions on this layer.
+    // Modes that require virtual identity later in G-code generation keep the
+    // original mixed ID; ordinary mixed rows collapse to the current physical
+    // extruder so adjacent same-tool regions can merge.
+    unsigned int effective_painted_region_filament_id(unsigned int filament_id,
+                                                      size_t       num_physical,
+                                                      int          layer_index,
+                                                      float        layer_print_z = 0.f,
+                                                      float        layer_height  = 0.f,
+                                                      float        layer_height_a = 0.f,
+                                                      float        layer_height_b = 0.f,
+                                                      float        base_layer_height = 0.2f) const;
     std::vector<unsigned int> ordered_perimeter_extruders(unsigned int filament_id,
                                                           size_t       num_physical,
                                                           int          layer_index,

src/libslic3r/PresetBundle.cpp

@@ -75,6 +75,7 @@ static std::vector<std::string> s_project_options {
     "mixed_filament_height_upper_bound",
     "mixed_filament_advanced_dithering",
     "mixed_filament_surface_indentation",
+    "mixed_filament_region_collapse",
     "mixed_filament_definitions",
     "mixed_color_layer_height_a",
     "mixed_color_layer_height_b",

src/libslic3r/Print.cpp

@@ -297,6 +297,7 @@ bool Print::invalidate_state_by_config_options(const ConfigOptionResolver & /* n
             || opt_key == "mixed_filament_height_upper_bound"
             || opt_key == "mixed_filament_advanced_dithering"
             || opt_key == "mixed_filament_surface_indentation"
+            || opt_key == "mixed_filament_region_collapse"
             || opt_key == "mixed_filament_definitions"
             // Spiral Vase forces different kind of slicing than the normal model:
             // In Spiral Vase mode, holes are closed and only the largest area contour is kept at each layer.

src/libslic3r/PrintApply.cpp

@@ -1112,18 +1112,22 @@ static inline void append_unique_painted_extruder(std::vector<unsigned int> &pai
         painting_extruders.emplace_back(extruder_id);
 }
 
-static void append_same_layer_component_extruders(const MixedFilamentManager &mixed_mgr,
-                                                  unsigned int                state_id,
-                                                  size_t                      num_physical_extruders,
-                                                  std::vector<unsigned int>  &painting_extruders)
+static void append_mixed_component_extruders(const MixedFilamentManager &mixed_mgr,
+                                             unsigned int                state_id,
+                                             size_t                      num_physical_extruders,
+                                             std::vector<unsigned int>  &painting_extruders)
 {
     if (state_id <= num_physical_extruders)
         return;
 
     const MixedFilament *mixed_row = mixed_mgr.mixed_filament_from_id(state_id, num_physical_extruders);
-    if (mixed_row == nullptr || !mixed_row->enabled || mixed_row->distribution_mode != int(MixedFilament::SameLayerPointillisme))
+    if (mixed_row == nullptr || !mixed_row->enabled)
         return;
 
+    // Pre-create painted target regions for every physical filament a mixed row
+    // may resolve to. apply_mm_segmentation can then collapse ordinary mixed
+    // channels onto the active physical tool for a layer without losing the
+    // destination region.
     append_unique_painted_extruder(painting_extruders, mixed_row->component_a, num_physical_extruders);
     append_unique_painted_extruder(painting_extruders, mixed_row->component_b, num_physical_extruders);
 
@@ -1177,6 +1181,7 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
     new_full_config.option("mixed_filament_pointillism_pixel_size", true);
     new_full_config.option("mixed_filament_pointillism_line_gap", true);
     new_full_config.option("mixed_filament_surface_indentation", true);
+    new_full_config.option("mixed_filament_region_collapse", true);
     new_full_config.option("mixed_filament_definitions", true);
     m_config.option("dithering_z_step_size", true);
     m_config.option("dithering_local_z_mode", true);
@@ -1188,6 +1193,7 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
     m_config.option("mixed_filament_pointillism_pixel_size", true);
     m_config.option("mixed_filament_pointillism_line_gap", true);
     m_config.option("mixed_filament_surface_indentation", true);
+    m_config.option("mixed_filament_region_collapse", true);
     m_config.option("mixed_filament_definitions", true);
     m_default_object_config.option("dithering_z_step_size", true);
     m_default_object_config.option("dithering_local_z_mode", true);
@@ -1199,6 +1205,7 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
     m_default_object_config.option("mixed_filament_pointillism_pixel_size", true);
     m_default_object_config.option("mixed_filament_pointillism_line_gap", true);
     m_default_object_config.option("mixed_filament_surface_indentation", true);
+    m_default_object_config.option("mixed_filament_region_collapse", true);
     m_default_object_config.option("mixed_filament_definitions", true);
     // BBS
     int used_filaments = this->extruders(true).size();
@@ -1772,10 +1779,10 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
                     continue;
                 if (state_idx <= num_total_filaments) {
                     painting_extruders.emplace_back(static_cast<unsigned int>(state_idx));
-                    append_same_layer_component_extruders(m_mixed_filament_mgr,
-                                                          static_cast<unsigned int>(state_idx),
-                                                          num_extruders,
-                                                          painting_extruders);
+                    append_mixed_component_extruders(m_mixed_filament_mgr,
+                                                     static_cast<unsigned int>(state_idx),
+                                                     num_extruders,
+                                                     painting_extruders);
                 } else
                     ++dropped_painted_states;
             }

src/libslic3r/PrintConfig.cpp

@@ -4244,6 +4244,15 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionFloat(0.0));
 
+    def = this->add("mixed_filament_region_collapse", coBool);
+    def->label = L("Collapse same-color mixed regions");
+    def->category = L("Others");
+    def->tooltip = L("Merge ordinary mixed-filament painted regions into a single area when they resolve to the same physical filament on a layer.\n\n"
+                     "This improves continuity for adjacent same-color areas. Local Z dithering turns this off automatically when enabled, but you may turn it back on manually.\n\n"
+                     "Experimental with Local Z dithering.");
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionBool(true));
+
     def = this->add("mixed_filament_definitions", coString);
     def->label = L("Mixed filament custom definitions");
     def->tooltip = L("Serialized custom mixed filament rows.\n\n"

src/libslic3r/PrintConfig.hpp

@@ -1363,6 +1363,7 @@ PRINT_CONFIG_CLASS_DERIVED_DEFINE(
     ((ConfigOptionFloat,              mixed_filament_pointillism_pixel_size))
     ((ConfigOptionFloat,              mixed_filament_pointillism_line_gap))
     ((ConfigOptionFloat,              mixed_filament_surface_indentation))
+    ((ConfigOptionBool,               mixed_filament_region_collapse))
     ((ConfigOptionString,             mixed_filament_definitions))
     ((ConfigOptionFloat,              dithering_z_step_size))
     ((ConfigOptionBool,               dithering_local_z_mode))

src/libslic3r/PrintObject.cpp

@@ -950,6 +950,7 @@ bool PrintObject::invalidate_state_by_config_options(
             || opt_key == "dithering_z_step_size"
             || opt_key == "dithering_local_z_mode"
             || opt_key == "dithering_step_painted_zones_only"
+            || opt_key == "mixed_filament_region_collapse"
             || opt_key == "mmu_segmented_region_max_width"
             || opt_key == "mmu_segmented_region_interlocking_depth"
             || opt_key == "raft_layers"
@@ -973,6 +974,7 @@ bool PrintObject::invalidate_state_by_config_options(
             || opt_key == "mixed_filament_height_upper_bound"
             || opt_key == "mixed_filament_advanced_dithering"
             || opt_key == "mixed_filament_surface_indentation"
+            || opt_key == "mixed_filament_region_collapse"
             || opt_key == "mixed_filament_definitions") {
             // Mixed filament gradient controls affect layer cadence and virtual
             // tool distribution, so force a re-slice prompt like other

src/libslic3r/PrintObjectSlice.cpp

@@ -2947,9 +2947,21 @@ template<typename ThrowOnCancel>
 static inline void apply_mm_segmentation(PrintObject &print_object, std::vector<std::vector<ExPolygons>> segmentation, ThrowOnCancel throw_on_cancel)
 {
     assert(segmentation.size() == print_object.layer_count());
+    const PrintConfig        &print_cfg = print_object.print()->config();
+    const DynamicPrintConfig &full_cfg  = print_object.print()->full_print_config();
+    const size_t              num_physical = print_cfg.filament_diameter.size();
+    const coordf_t            preferred_a = float_from_full_config(full_cfg, "mixed_color_layer_height_a",
+                                                                   coordf_t(print_cfg.mixed_color_layer_height_a.value));
+    const coordf_t            preferred_b = float_from_full_config(full_cfg, "mixed_color_layer_height_b",
+                                                                   coordf_t(print_cfg.mixed_color_layer_height_b.value));
+    const coordf_t            base_height = std::max<coordf_t>(0.01f, coordf_t(print_object.config().layer_height.value));
+    const bool                collapse_mixed_regions =
+        bool_from_full_config(full_cfg, "mixed_filament_region_collapse", print_cfg.mixed_filament_region_collapse.value);
+    const MixedFilamentManager &mixed_mgr = print_object.print()->mixed_filament_manager();
+
     tbb::parallel_for(
         tbb::blocked_range<size_t>(0, segmentation.size(), std::max(segmentation.size() / 128, size_t(1))),
-        [&print_object, &segmentation, throw_on_cancel](const tbb::blocked_range<size_t> &range) {
+        [&print_object, &segmentation, &mixed_mgr, num_physical, preferred_a, preferred_b, base_height, collapse_mixed_regions, throw_on_cancel](const tbb::blocked_range<size_t> &range) {
             const auto  &layer_ranges   = print_object.shared_regions()->layer_ranges;
             double       z              = print_object.get_layer(int(range.begin()))->slice_z;
             auto         it_layer_range = layer_range_first(layer_ranges, z);
@@ -2982,7 +2994,20 @@ static inline void apply_mm_segmentation(PrintObject &print_object, std::vector<
                 size_t missing_target_regions = 0;
                 std::vector<int> missing_target_extruders;
                 for (size_t extruder_id = 0; extruder_id < num_extruders; ++ extruder_id) {
-                    ByExtruder &region = by_extruder[extruder_id];
+                    const unsigned int channel_id = unsigned(extruder_id + 1);
+                    const unsigned int effective_filament_id = collapse_mixed_regions ?
+                        mixed_mgr.effective_painted_region_filament_id(channel_id,
+                                                                       num_physical,
+                                                                       int(layer_id),
+                                                                       float(layer.print_z),
+                                                                       float(layer.height),
+                                                                       float(preferred_a),
+                                                                       float(preferred_b),
+                                                                       float(base_height)) :
+                        channel_id;
+                    const size_t effective_idx =
+                        effective_filament_id >= 1 && effective_filament_id <= num_extruders ? size_t(effective_filament_id - 1) : extruder_id;
+                    ByExtruder &region = by_extruder[effective_idx];
                     append(region.expolygons, std::move(segmentation[layer_id][extruder_id]));
                     if (! region.expolygons.empty()) {
                         region.bbox = get_extents(region.expolygons);

src/slic3r/GUI/Tab.cpp

@@ -1491,6 +1491,21 @@ void Tab::on_value_change(const std::string& opt_key, const boost::any& value)
         update_wiping_button_visibility();
     }
 
+    if (opt_key == "dithering_local_z_mode" &&
+        boost::any_cast<bool>(value) &&
+        (!m_config->has("mixed_filament_region_collapse") ||
+         m_config->option("mixed_filament_region_collapse") == nullptr ||
+         m_config->opt_bool("mixed_filament_region_collapse"))) {
+        change_opt_value(*m_config, "mixed_filament_region_collapse", boost::any(false));
+        if (m_type == Preset::TYPE_PRINT) {
+            DynamicPrintConfig &project_cfg = wxGetApp().preset_bundle->project_config;
+            project_cfg.set_key_value("mixed_filament_region_collapse", new ConfigOptionBool(false));
+        }
+        if (Field *field = this->get_field("mixed_filament_region_collapse"))
+            field->set_value(boost::any(false), false);
+        update_dirty();
+    }
+
 
     if (opt_key == "single_extruder_multi_material"  ){
         const auto bSEMM = m_config->opt_bool("single_extruder_multi_material");
@@ -1791,6 +1806,7 @@ void Tab::on_value_change(const std::string& opt_key, const boost::any& value)
          opt_key == "mixed_filament_pointillism_pixel_size" ||
          opt_key == "mixed_filament_pointillism_line_gap" ||
          opt_key == "mixed_filament_surface_indentation" ||
+         opt_key == "mixed_filament_region_collapse" ||
          opt_key == "dithering_z_step_size" ||
          opt_key == "dithering_local_z_mode" ||
          opt_key == "dithering_step_painted_zones_only" ||
@@ -2528,6 +2544,7 @@ optgroup->append_single_option_line("skirt_loops", "others_settings_skirt#loops"
         optgroup->append_single_option_line("mixed_filament_pointillism_pixel_size");
         optgroup->append_single_option_line("mixed_filament_pointillism_line_gap");
         optgroup->append_single_option_line("mixed_filament_surface_indentation");
+        optgroup->append_single_option_line("mixed_filament_region_collapse");
         optgroup->append_single_option_line("dithering_z_step_size");
         optgroup->append_single_option_line("dithering_local_z_mode");
         optgroup->append_single_option_line("dithering_step_painted_zones_only");

tests/libslic3r/test_mixed_filament.cpp

@@ -221,6 +221,41 @@ TEST_CASE("Mixed filament perimeter resolver uses grouped manual patterns by ins
     CHECK(ordered_layer1[1] == 1);
 }
 
+TEST_CASE("Mixed filament painted-region resolver collapses ordinary mixed rows to the active physical extruder", "[MixedFilament]")
+{
+    const std::vector<std::string> colors = {"#FF0000", "#00FF00"};
+
+    MixedFilamentManager mgr;
+    mgr.add_custom_filament(1, 2, 50, colors);
+    REQUIRE(mgr.mixed_filaments().size() == 1);
+
+    MixedFilament &row = mgr.mixed_filaments().front();
+    row.ratio_a = 1;
+    row.ratio_b = 1;
+    row.manual_pattern.clear();
+    row.distribution_mode = int(MixedFilament::Simple);
+
+    CHECK(mgr.effective_painted_region_filament_id(3, 2, 0) == 1);
+    CHECK(mgr.effective_painted_region_filament_id(3, 2, 1) == 2);
+}
+
+TEST_CASE("Mixed filament painted-region resolver preserves virtual channels for grouped and same-layer modes", "[MixedFilament]")
+{
+    const std::vector<std::string> colors = {"#00FFFF", "#FF00FF"};
+
+    MixedFilamentManager mgr;
+    mgr.add_custom_filament(1, 2, 50, colors);
+    REQUIRE(mgr.mixed_filaments().size() == 1);
+
+    MixedFilament &row = mgr.mixed_filaments().front();
+    row.manual_pattern = MixedFilamentManager::normalize_manual_pattern("12,21");
+    CHECK(mgr.effective_painted_region_filament_id(3, 2, 0) == 3);
+
+    row.manual_pattern.clear();
+    row.distribution_mode = int(MixedFilament::SameLayerPointillisme);
+    CHECK(mgr.effective_painted_region_filament_id(3, 2, 0) == 3);
+}
+
 TEST_CASE("ExtrusionPath copies preserve inset index", "[MixedFilament]")
 {
     ExtrusionPath src(erPerimeter);